When the same monochromatic ray of light travels through glass slab and through water, the number of waves in glass slab of thickness $6 \mathrm{cm}$ is same as in water column of height $7 \mathrm{cm}$. If refractive index of glass is $1.5$, then refractive index of water is, 

$v_0$ and $v_{\mathrm{E}}$ represent the velocities, ${\mu }_0$ and ${\mu }_{\mathrm{E}}$ the refractive indices of ordinary and extraordinary rays for a doubly refracting crystal. Then

Through which character we can distinguish the light waves from sound waves?

Which of the following cannot be polarised? 

In the propagation of electromagnetic waves, the angle between the direction of propagation and plane of polarisation is 

When a plane polarised light is passed through an analyser and analyser is rotated through $90^{\circ},$ the intensity of the emerging light 

A beam of light $A O$ is incident on a glass slab $(\mu=1.54)$ in a direction as shown in figure. The reflected ray $OB$ is passed through a Nicol prism. On view through a Nicol prism, we find on rotating the prism that

An optically active compound 

From Brewster's law, except for polished metallic surfaces, the polarising angle